Torque motor-driven spool valves are well known in the art including such which operate through the utilization of a rotary torque motor having a drive member extending from the rotor thereof into contact with the spool valve to directly reciprocate the spool valve within a bore provided in the valve housing to thereby control the flow of fluid from a source thereof to the load in response to electrical signals applied to the drive motor. Typical of such direct drive servovalves is that illustrated in U.S. Pat. No. 4,793,377 issued Dec. 27, 1988, to Larry E. Haynes et al. The invention described and claimed herein is an improvement over the direct drive servovalve disclosed in U.S. Pat. No. 4,793,377 and therefore the disclosure of U.S. Pat. No. 4,793,377 is incorporated herein by this reference.
Other prior art known to applicants are U.S. Pat. Nos. 4,197,474; 2,769,943; 2,697,016; 4,452,423; 4,339,737 and 4,702,123 as well as Canadian Patent 601,808 issued July 19, 1960, and United Kingdom Patent 1,521,668 issued Aug. 16, 1978.
It is critical in direct drive servovalves that the drive member of the drive motor be properly aligned with the spool valve to obtain the desired control of the flow of fluid by the spool valve. In prior-art valves, it has been traditional to hold strict tolerances with respect to bearing/housing concentricities, base/housing concentricities, flange mounting holes, as well as the rotor shaft and other components of the motor assembly in order to provide the correct alignments. The strict attention to these tolerances both during manufacture and assembly of the direct drive servovalves necessarily adds to the expense and difficulty of manufacture thereof. Furthermore, it becomes extremely difficult to disassemble such valves for repair and/or maintenance and then reassemble them while maintaining the desired alignments and tolerances.